Positive Displacement Pumping Chamber

ABSTRACT

A substrate processing system as illustrated at ( 1 ). A substrate ( 2 ) lies upon a piston ( 3 ) shown in both the loading position ( 3   a ) and in a processing position ( 3   b ). The substrate is loaded via a port ( 4 ) through a door ( 5 ). The loading area ( 7   a ), and/or the hole chamber ( 7 ) may be pumped out via a vacuum exhaust pipe ( 6 ) connected to a pump (not shown). A linear drive mechanism shown diagrammatically at ( 8 ) lifts the piston and the substrate in the chamber such that a process volume ( 7   b ) of the chamber is defined with poor gas conduction between the piston and the walls of the chamber.

The present invention describes an apparatus for the deposition and/orremoval of thin layers of materials on or from a substrate such as asilicon wafer. A number of advanced deposition and etching processesmake use of discrete steps for the formation of a thin film or theetching of deep structures. These steps are preferably performed in oneprocess chamber (either batch or single wafer).

By way of example, Atomic Layer deposition (ALD—also known as atomiclayer epitaxy) is a chemical vapor deposition process in whichself-limiting surface reactions produce extremely conformal coatings.There is a growing requirement to increase equipment productivity forALD and similar processes for example to form very thin layers highdielectric constant (k) films such as HfO₂ or alumina. For the ALD of alayer such as Aluminum oxide a reactant gas containing Aluminum such astrimethyl aluminum Al(CH₃)₃ is firstly introduced into a chambercontaining the substrate(s) such that a monolayer of this gas adheres toand in many cases saturates the surface. A purge is then necessary bypumping only or with an inert (to this process) gas such as nitrogen orhydrogen to remove all but this monolayer of gas from the chamber. Thenan oxidizer, such as water vapor, is flowed into the chamber and asurface reaction with the trimethyl aluminum takes place forming amonolayer of aluminum oxide. Excess oxidizer and reaction by-productsare then pumped away and the chamber purged and the cycle repeated untilthe desired film thickness achieved.

The cycle time therefore=Exposure A+Purge A+Exposure B+Purge B

Purge is used throughout to mean the sufficient removal or dilution ofthe reactant. This may be achieved by pumping alone or by pumping andflowing an inert (Purge) gas or any sequence of the two as is well knownin the field.

Where A and B represent the precursors from which the deposited film isderived. This is example is given simply by way of example and a reviewof the field will give many further examples of such step-wisedeposition processes.

Whilst this binary process produces high quality films and is relativelyinsensitive to other process parameters it is very slow, as the layersare built up monolayer at a time.

The necessary exposure time is very short so a known attractive approachto increasing the speed of film growth is to decrease exposure times.Whilst exposure times may be reduced to very short periods e.g. sub 1second, it is a critical requirement that the process chamber isadequately purged after the precursor exposure steps.

Presently there is no method of reducing the purge times to those asshort as the exposure times and in an otherwise optimized processperhaps 75% of the total cycle time is spent (unproductively) purgingthe chamber.

A method of rapidly extracting the process chamber gaseous contentswould therefore be advantageous as it would increase the productivity ofequipment for ALD and other stepwise processes.

From one aspect the invention consists in apparatus for processing asubstrate in a process cycle including a chamber for receiving asubstrate in a process volume and a moveable wall displaceable to varythe process volume in accordance with the process cycle.

The apparatus may include an exhaust outlet and the moveable wall may bemoveable to reduce the process volume to purge gas from the processvolume through the exhaust outlet during a purge part of the processcycle. In a particularly preferred embodiment there are a plurality ofexhaust valves operable in respect purge parts of the process cycle.

Similarly the apparatus may include an inlet for process gas and themoveable wall may be moveable to draw process gas through the inletduring the process part of the process cycle. There may be a pluralityof inlet valves for respective process gases.

There may also be an inlet for purge gas and the purge gas inlet may beconstituted by a process gas inlet.

The ratio of the largest and smallest process volumes defined by themoveable wall may be between about 5:1 and 100:1. In a particularlypreferred arrangement the volume ratio is about 10:1.

The compression ratio in the process volume resulting from the movementof the wall may be about between 5:1 and about 100:1 and 10:1 isparticularly preferred.

The moveable wall may act as or carry a substrate support, in which casethe moveable wall may additionally be moveable between a substrateload/unload position and a process chamber defining position.

The moveable wall may be located in an extension of the process chamber,in which case the chamber and the extension may have a common housing.Additionally or alternatively the extension may be adjacent the chamber.

In an alternative embodiment the apparatus may include a substratesupport and the moveable wall may be generally opposite to the substratesupport. In this case the apparatus may include a fixed housingextending around the substrate support to define a process chambertogether with the moveable wall and support. The moveable wall and/orhousing may include a plurality of parts, at least two of which arerelatively moveable to allow loading of a substrate onto the substratesupport.

In any of the above cases the wall may be a piston.

In another aspect the invention may consist in a method of processing asubstrate including placing the substrate in a process volume andintroducing a process gas or vapour into the process volume and/orsubsequently removing gas or vapour from the volume wherein the step ofintroducing and/or removing the gas is at least partially performed bymoving a moveable wall to change the process volume in an appropriatesense.

The steps of introducing and removing may be sequentially repeated.

The process performed may be chemical vapour deposition such as atomiclayer deposition or dry etching or any other suitable process.

The afore mentioned apparatus may include a controller for operatingthat apparatus in accordance with any of the above defined methods.

In a further aspect the invention consists in a substrate processchamber with a moving wall such as a piston wherein the process volumeis changed to increase the efficiency of exposure to, or purging ofprecursors.

The moving wall may be a piston or diaphragm and may move in cooperationwith the timing of an inlet or outlet valve.

Inlet and exhaust valves, (which may be piston ported) may be used forthe inlet and outlet of the reactants and purge gas. By this means thevapor or gas within the chamber may be positively displaced by movingthe wall to increase the speed of their removal and/or their volumedecreased (pressure increased) to speed evacuation from the processchamber. Also, by being able to increase the process volume the pressureof a fixed mole volume of gas may be reduced and thereby the speed ofdistribution of a gas charge across a substrate be increased.

In another aspect the invention consists of a method of removing ordistributing gas or vapor contents from or within a chemical vapordeposition reaction chamber by moving a wall such that the chambervolume is changed.

By changing the process volume the pressure of a fixed quantity of gasis changed and it is then possible to exploit different gas flow dynamiccharacteristics at different steps of the step-wise process. So, forexample, the chamber pressure can be rapidly reduced by rapidlyincreasing its volume by rapidly moving the wall. Similarly a fixed gascharge may be removed from the chamber more quickly for any givenconductivity pipe work by reducing its volume/increasing its pressure.Additionally the moving of a wall to reduce the chamber volumepositively displaces the fluid contents of the chamber.

Exploiting the different gas flow dynamics at different pressures alsoallows for advantageous changes in inlet and outlet valving and entryand exit points and may allow for smaller exhaust valves and pipe workand allow for simpler gas injection systems with fewer gas injectionholes.

Rapid pump-purge cycles are also achievable by the use of this movingwall and in a further aspect of the invention there is provided at least2 chamber exhaust ducts to segregate the first precursor exhaust fromthe second precursor exhaust thereby enabling precursor recycling.

Whilst chemical vapor deposition, and in particular atomic layerdeposition processes have been described, the apparatus and methods mayalso be applied to other step-wise processes such as in the field of dryetching, including plasma etching of substrates and in particularcomposite deposition/etch processes such as the deep etching of silicon,such as the ‘Bosch’ process.

The substrate may be a silicon or compound wafer, glass, polymer or discdrive head and the structures formed may be part of microelectronic,magnetic, radio or photonic devices such as memory or logic devices,displays, emitters, sensors and storage devices including discs or reador write heads.

Although the invention has been defined above, it is to be understood itincludes an inventive combination of the features set out above or itthe following description.

The invention may be performed in various ways and specific embodimentswill now be described, by way of example with reference to the followingdrawings in which:

FIG. 1 is a diagram of an embodiment of the invention;

FIG. 2 is a diagram of parts of another embodiment of the invention;

FIG. 3 is a diagram of another embodiment of the invention; and

FIG. 4 is a matrix indicating a piston valve sequence for the depositionof metal oxide.

A substrate processing system is shown in FIG. 1 generally at 1. Asubstrate 2 lies upon a piston 3 shown in both a loading position 3 aand in a processing position 3 b. A substrate is loaded via a port 4with a door 5 if required. The loading area 7 a and or the whole chamber7 may be pumped out via vacuum exhaust pipe 6 connected to a pump (notshown) and this pipe work may provide vacuum pumping at the underside ofthe piston 3 when at its processing position 3 b (the piston effectivelyvalving off vacuum exhaust 6 from the process volume 7 b).

Linear drive mechanism (such as a crank) shown diagrammatically at 8lifts the piston and substrate in the chamber such that a process volume7 b of the chamber is defined with poor gas conduction between thepiston and the walls of the chamber. The linear drive then moves thepiston up and down at programmed speeds and distances and gas or vapoursare input to the chamber via inlet valves 9 and exhausted via outletvalves 10 where the exhausted gas may pass via pipe 11 to an extract orwaste management system that most preferably may recycle at least partof one process gas back to valve 9.

A purge gas inlet (not shown) may also be provided to provide purge gasto the underside of the piston in its processing position. It should beunderstood that the exhaust valve 10 may be optional, depending on thevacuum pumping arrangement. Its main function may be to stop exhaustbeing sucked back into the process chamber when the piston rapidlyexpands the chamber volume. It may also be necessary, when the piston ismoved to reduce the process volume.

It should be understood that the piston 3 may rotate or oscillaterotationally if desired to improve process and/or sealing of the pistonto the chamber wall. The piston may include a wafer clamp means such asan electrostatic force or clips or clamping ring and may be flat orrecessed as is desired.

Whilst the chamber is shown diagrammatically as a unit, it may be madeof many parts of differing materials and in particular may have adielectric wall about process volume 7 b. Radio frequency power may beapplied e.g. by antenna 13 to enable plasma processing such as acleaning process for the substrates or the chamber or during depositionor etching of a substrate.

FIG. 2 shows parts for an alternative embodiment of the invention wherethe substrate platen 30 does not rise and fall during processing andinstead an opposing closed ended cylinder 40 driven by a linear driveshown diagrammatically at 50 achieves the positive displacement of gasor vapour. Cylinder 40 (or an upper part thereof) is lifted to allow asubstrate to be placed upon the platen 30 that may advantageously becontrolled to a process temperature and also has a method of clampingthe substrate such as electrostatically or mechanically. The cylinder(or upper part thereof) then lowers about a lower assembly 60 thatsurrounds the platen and contains inlet(s) 70 and outlet(s) 80 for theprocess and purge gasses or vapours. There is a low conductance path (orgas seal) between complete cylinder 40 and lower assembly 60 when thecylinder is in the lowered position. The cylinder 40 may consist of 2parts, one of which is permanently about the lower assembly e.g. mountedon a bearing such that the upper part of the cylinder lowers and engagesand seals with the lower cylinder part. By driving the cylinder 40 upand down about lower assembly 60 positive gas displacement is achievedwithin the working volume of the chamber defined by the cylinder 40 andthe lower assembly 60 and containing gas inlets 70 and outlets 80. Thecylinder 40 is contained more generally within a vacuum or controlledatmosphere 90.

The advantage of this embodiment is that the substrate platen is notmoved and thereby complex platens such as heated or chilled ceramicplatens with tight temperature control and electrostatic clamping aremore easily built.

It should also be understood that the piston or moving wall need notoppose the substrate but may be in any location such that its movementmakes a significant change in the process volume.

It will also be understood that the more remote the piston is from theactual chamber, the larger the effective process volume becomes as theconnection between the chamber and the piston effectively become part ofthe process volume. This means that the volume swept by the piston needsto increase in order to effect suitable pressure changes in the processvolume and in practice it will usually be necessary for the piston to beeither within the chamber or substantially adjacent to it.

FIG. 3 shows another embodiment where the piston 3 (driven linearly by adrive mechanism 8) is closely coupled to the substrate 2 lying upon aplaten 14. The substrate is loaded via a port 4 with a door 5 in thechamber 7. Gas inlet valve 9 and outlet valve 10 are provided wherethere may be more than one inlet and/or outlet valve to separate theinput precursors and if a separate exhaust 11 is provided for one of theprecursors then this may take the exhaust to a recovery and recyclingsystem (not shown). The underside area 15 of the piston may be eitherlarge compared to the process volume 7 and/or connected to inlet/outletmeans to allow free movement of the piston.

The piston may move up (reduced process volume) one or more times tocompress and/or expel chamber fluid contents and may move down (increaseprocess volume) one or more times to reduce process volume pressure ordraw in or fill the chamber. The movement of the piston may createturbulence and/or reduce pressure and thereby increase the speed of gasinjected non-uniformly to move about the chamber and thereby coat thesubstrate surface more uniformly.

The piston or wall may move rapidly and affect a chamber purge in lessthan one second.

The opening and closing of valves may be timed to the piston movement bymechanical or electrical or electronic means. The piston may be on acrank or may be driven such as by a linear motor. The speed and distanceof travel and number of strokes of the piston may be the same or bevarying for the different steps of the cyclic process as is foundnecessary to optimize the process. FIG. 3 shows, by way of example, apiston/valves sequence matrix useable in a metal oxide depositionprocess.

In other cases the piston may only move for a purge step such as betweenoxidation and the metal containing precursor introduction to thechamber.

The reactants may be vaporized and injected or pumping into the chamberas a vapor or they may be atomized or vaporized at the point ofdispensation into the chamber and it is to be understood that the use ofa purge gas is optional.

The reactants can be energized if desired before entering the chambersuch as by heat, radio, light or some other electromagnetic frequency.

The reactants and purge gasses may be recovered, filtered, purified andmade up with fresh reactant and recirculated to reduce consumption.

The compression ratio of the apparatus will determine the peakprocessing pressure and this may be varied between gases, cycles andthroughout a deposition as is desirable particularly if a linear motordrive is chosen for the piston. Pressure, as well as temperature andother process requirements may be sensed and the results fed back to acontrol system to provide process control.

The face opposing the substrate may be shaped to improve gasdistribution to improve process or efficiency characteristics such asuniformity of deposition and efficiency of gas consumption.

By way of example for a 300 mm diameter chamber with a working spacingof 10 mm that compresses to 1 mm spacing.

Representative Values:

Time for chamber wall to move between 10 mm and 1 mm spacing: 0.1 second

Process spacing: 10 mm Process pressure:  1 torr

For a 1 torr process pressure at the 10 mm spacing then when compressedto a 1 mm spacing there will be approximately 70 ccs of gas at 10 torrpressure.

Vacuum simulation software tells us that it will take 0.22 secs toexhaust to 100 mT with an exhaust gas outlet of 0.5 inches diameter.This assumes that the exhaust is only open when the chamber iscompressed to 1 mm whereas evacuation will be faster if the exhaustvalve is open throughout this compression stroke. Moving the chamberspacing back to 10 mm from 1 mm then drops the pressure by a factor of10 to 10 mT.

With 0.2 secs for piston movement (up and down) and 0.22 secs exhausttime at 1 mm spacing there is a total time of 0.42 secs to take thechamber from 1 Torr to 10 mT at 10 mm spacing by this combination ofcompression and expansion and evacuation.

Without moving the chamber wall and simply pumping by opening the samesize exhaust will take 3 seconds computed by the same software model tothe same assumptions.

For superior purging of a chamber a purge gas may be introduced as wellas pumping. This procedure may also advantageously be carried out with achanging in chamber volume as herein described.

If 100:1 dilution is not enough and 1000:1 is desired, then pumping theuncompressed volume to 1 mTorr takes an extremely long time even withvery large diameter pipework and valves and very high speed low pressurepumps. By just pumping, each extra decade in base pressure of a reactantincreases time in a very non-linear fashion. But with a positivedisplacement chamber the time to get another decade in base pressure islinear. So, for example, twice the time, i.e. 0.84 seconds provides10000:1 dilution . . . 1.26 seconds provides 1000000:1 . . . etc.

1. Apparatus for processing a substrate in a process cycle comprising: achamber for receiving a substrate in a process volume and a movable walldisplaceable to vary the process volume in accordance with the processcycle.
 2. Apparatus as claimed in claim 1 including an exhaust outletand wherein the movable wall can be moved to reduce the process volumeto purge gas from the process volume through the exhaust outlet during apurge part of the process cycle.
 3. Apparatus as claimed in claim 2wherein there are a plurality of exhaust valves operable in respectivepurge parts of the process cycle.
 4. Apparatus as claimed in claim 1including an inlet for process gas and wherein the movable wall ismovable to draw process gas through the inlet during a process part ofthe process cycle.
 5. Apparatus as claimed in claim 4 wherein there area plurality of inlet valves for respective process gases.
 6. Apparatusas claimed in claim 1 including an inlet for purge gas.
 7. Apparatus asclaimed in claim 6 wherein the purge gas inlet is a process gas inlet.8. Apparatus as claimed in claim 1 wherein the ratio of the largest andsmallest process volumes defined by the movable wall is between about5:1 and about 100:1.
 9. Apparatus as claimed in claim 8 wherein thevolume ratio is about 10:1.
 10. Apparatus as claimed in claim 1 whereinthe compression ratio in the process volume resulting from movement ofthe wall is between about 5:1 and about 100:1.
 11. Apparatus as claimedin claim 10 wherein the compression ratio is about 10:1.
 12. Apparatusas claimed in claim 1 wherein the movable wall acts as or carries asubstrate support.
 13. Apparatus as claimed in claim 12 wherein themovable wall is additionally movable between a substrate load/unloadposition and a process chamber defining position.
 14. Apparatus asclaimed in any claim 1 wherein the movable wall is located in anextension of the process chamber.
 15. Apparatus as claimed in claim 14wherein the chamber and the extension have a common housing. 16.Apparatus as claimed in claim 14 or claim 15 wherein the extension isadjacent the chamber.
 17. Apparatus as claimed in claim 1 including asubstrate support and wherein the movable wall is generally opposite tothe substrate support.
 18. Apparatus as claimed in claim 17 furtherincluding a fixed housing extending around the substrate support todefine a process chamber together with the removable wall and substratesupport.
 19. Apparatus as claimed in claim 17 or claim 18 wherein themoveable wall and/or housing includes a plurality of parts at least twoof which are relatively moveable to allow loading of a substrate ontothe substrate support.
 20. Apparatus as claimed in any one of thepreceding claims wherein the wall is a piston.
 21. A method ofprocessing a substrate comprising: placing the substrate in a processvolume and introducing a process gas or vapour into the process volumeand/or subsequently removing gas or vapour from the volume wherein thestep of introducing and/or removing the gas is at least partiallyperformed by moving a movable wall to change the process volume in anappropriate sense.
 22. A method as claimed in claim 21 wherein the stepsof introducing and removing are sequentially repeated.
 23. A method asclaimed in claim 21 or claim 22 wherein the process is chemical vapourdeposition.
 24. A method as claimed in claim 23 wherein the process isatomic layer deposition.
 25. A method as claimed in claim 21 or claim 22wherein the process is dry etching.
 26. Apparatus as claimed in claim 1including a controller for operating the apparatus in accordance withthe method of claim 25.